Th17 cell and inflammatory cytokine (IL-17A, IL-17F, etc.) produced thereby cause a decrease in QOL as a severe etiology cell and factor accompanying enhancement of a systemic new immune response, in various autoimmune disease such as inflammatory bowel disease (IBD), rheumatoid arthritis, multiple sclerosis or psoriasis. However, the existing therapeutic drugs show only limited effects, and therefore, the earliest possible development of a novel therapeutic drug has been desired.
Involvement of T cells, inter alia, Th17 cell and inflammatory cytokines (IL-17A, IL-17F, etc.) produced thereby, in the pathology of these immune disease has been drawing attention in recent years.
Moreover, it has been recently clarified that a Retinoid-related Orphan Receptor (ROR) γt, which is one of the orphan nuclear receptors, plays an important role in the differentiation of Th17 cells and production of IL-17A/IL-17F. That is, it has been reported that RORγt is mainly expressed in Th17 cells and functions as a transcription factor of IL-17A and IL-17F, as well as a master regulator of Th17 cell differentiation.
Therefore, a medicament that inhibits the action of RORγt is expected to show a treatment effect on various immune diseases by suppressing differentiation and activation of Th17 cells.
As a compound having a nitrogen-containing fused heterocyclic structure, for example, the following benzoxazine compounds are reported.

Patent Document 1 reports a compound represented by the formula (I):
whereinR1 is C1-6 alkyl, C2-6 alkynyl, C3-6 cycloalkyl, hydroxy-C1-6 alkyl or C1-3 alkoxy-C1-6 alkyl;R2 is NR8R9, —O—C1-6-alkylene-NR4R5, —O—C1-6 alkylene-CONR4R5, —O—C1-6 alkylene-CO2R6 or the like; andW is C1-3 alkylene or C2-3 alkynylene.
In addition, as a pyrido[2,3-d]pyrimidine compound, the following compounds are known.
